The present invention relates to a vehicle seat including a pivoting back that is urged forwards by a torsion bar.
More particularly, the invention provides a vehicle seat comprising two opposite sides, the seat including a back mounted on a seat proper to pivot about a transverse horizontal pivot axis by means of a locking mechanism that can be moved between a locked position in which said locking mechanism prevents the back from moving relative to the seat proper, and an unlocked position in which said locking mechanism leaves the back free to pivot relative to the seat proper about the pivot axis, the back being urged forwards by means of a torsion bar constituted by a metal wire which has two ends fixed respectively to the back and to the seat proper, at respective ones of the opposite sides of the seat.
Document JP-A-10 157 500 describes an example of such a seat. Torsion bars of the kind used in the seat of that document nevertheless suffer from the drawback of producing satisfactory return torque only over a relatively small angular stroke for the back.
A particular object of the present invention is to mitigate that drawback.
To this end, the invention provides a seat of the kind in question which is characterized in that the metal wire constituting the torsion bar forms at least one spiral including a plurality of adjacent turns.
By means of these dispositions, the equivalent length of the torsion bar is increased, thereby enabling said torsion bar to produce satisfactory return torque over a wide range of angular positions of the seat back.
In preferred embodiments of the invention, one or more of the following dispositions may optionally be used:
the torsion bar has a central portion extending substantially parallel to the pivot axis between first and second lever arms each extending in a general direction that is substantially perpendicular to the pivot axis, the spiral being formed between the central portion and the first lever arm, and said spiral having a central axis that is disposed perpendicularly to the central portion of the torsion bar and that is offset from said central portion of the torsion bar by a certain non-zero distance;
the turns of the torsion bar all have the same diameter substantially equal to twice said offset distance between the central axis of the spiral and the central portion of the torsion bar;
the spiral comprises:
a first turn which includes an initial portion extending upwards over 90xc2x0 between a segment having a horizontal tangent disposed in line with the central portion of the torsion bar, and a segment having a vertical tangent; and
a last turn which includes an end portion extending upwards over 90xc2x0 between a segment having a horizontal tangent and a segment having a substantially vertical tangent and disposed in line with the first lever arm;
the spiral comprises a portion adjacent to the central portion of the torsion bar in which the turns touch one another, and a portion which is remote from said central portion of the torsion bar and in which the turns are spaced apart from one another;
the spiral comprises three turns;
the spiral presents a developed length lying in the range 30% to 62.5% of the length of the central portion of the torsion bar;
the back is adapted to pivot relative to the seat proper over an angular stroke of magnitude lying in the range 120xc2x0 to 180xc2x0;
the back is adapted to pivot relative to the seat proper between a xe2x80x9ctablexe2x80x9d position in which said back is folded down substantially horizontally over the seat proper, and a xe2x80x9cbunkxe2x80x9d position in which the back is tilted rearwards into a substantially horizontal position; and
the metal wire is a steel wire presenting a diameter lying in the range 6 millimeters (mm) to 9 mm, the central portion of the torsion bar presenting a length lying in the range 40 centimeters (cm) to 50 cm, and the spiral presenting a developed length lying in the range 15 cm to 25 cm.